The Replacement of Fish Meal with Poultry By-Product Meal and Insect Exuviae: Effects on Growth Performance, Gut Health and Microbiota of the European Seabass, Dicentrarchus labrax

This study addressed the urgent need for sustainable protein sources in aquaculture due to the depletion of marine resources and rising costs. Animal protein sources, particularly poultry by-product meal (PBM) and insect exuviae meal, were investigated as viable alternatives to fishmeal (FM). The research study confirmed the successful replacement of FM with a combination of PBM and insect exuviae meal (up to 50%) in the diet of European seabass without compromising growth, feed conversion, gut health, and liver fat content. In particular, growth was robust with both PBM formulations, with the 25% PBM diet showing better results. Histological examinations showed good gut and liver health, contradicting the concerns of previous studies. This paper emphasizes the importance of holistic analyzes that go beyond growth parameters and include histomorphological investigations. The results show that PBM in combination with insect/exuviae meal is well tolerated by seabass, which is consistent with reports in the literature of it mitigating negative effects on gut health. A detailed analysis of the microbiota revealed a decrease in the Firmicutes/Proteobacteria ratio due to an increase in potentially pathogenic bacteria. However, the formulation containing insect exuviae partially counteracted this effect by preserving the beneficial Lactobacillus and promoting the synthesis of short-chain fatty acids (SCFAs), particularly butyrate. Chitin-rich components from insect exuviae were associated with improved gut health, which was supported by the increased production of SCFAs, which are known for their anti-inflammatory properties. This paper concludes that a combination of PBM and insect/exuviae meal can replace up to 50% of FM in the diet of seabass, supporting sustainable aquaculture practices. Despite some changes in the microbiota, the negative effects are mitigated by the addition of insect exuviae, highlighting their potential as a prebiotic to increase fish productivity and contribute to a circular economy in aquaculture.

The impact of diets containing Hermetia illucens meal on the growth, intestinal health, and microbiota of gilthead seabream (Sparus aurata)

The present study investigated the effect of replacing fishmeal (FM) with insect meal of Hermetia illucens (HI) in the diet of Sparus aurata farmed inshore on growth, gut health, and microbiota composition. Two isolipidic (18% as fed) and isoproteic (42% as fed) diets were tested at the farm scale: a control diet without HI meal and an experimental diet with 11% HI meal replacing FM. At the end of the 25-week feeding trial, final body weight, specific growth rate, feed conversion rate, and hepatosomatic index were not affected by the diet. Gross morphology of the gastrointestinal tract and the liver was unchanged and showed no obvious signs of inflammation. High-throughput sequencing of 16S rRNA gene amplicons (MiSeq platform, Illumina) used to characterize the gut microbial community profile showed that Proteobacteria, Fusobacteria, and Firmicutes were the dominant phyla of the gut microbiota of gilthead seabream, regardless of diet. Dietary inclusion of HI meal altered the gut microbiota by significantly decreasing the abundance of Cetobacterium and increasing the relative abundance of the Oceanobacillus and Paenibacillus genera. Our results clearly indicate that the inclusion of HI meal as an alternative animal protein source positively affects the gut microbiota of seabream by increasing the abundance of beneficial genera, thereby improving gut health and maintaining growth performance of S. aurata from coastal farms.

Polychaete (Alitta virens) meal inclusion as a dietary strategy for modulating gut microbiota of European seabass (Dicentrarchus labrax)

Recent research has revealed the significant impact of novel feed ingredients on fish gut microbiota, affecting both the immune status and digestive performance. As a result, analyzing the microbiota modulatory capabilities may be a useful method for assessing the potential functionality of novel ingredients. Therefore, this study aimed to evaluate the effects of dietary polychaete meal (PM) from Alitta virens on the autochthonous and allochthonous gut microbiota of European seabass (Dicentrarchus labrax). Two diets were compared: a control diet with 25% fishmeal (FM) and a diet replacing 40% of fishmeal with PM, in a 13-week feeding trial with juvenile fish (initial weight of 14.5 ± 1.0 g). The feed, digesta, and mucosa-associated microbial communities in fish intestines were analyzed using high-throughput sequencing of the 16S rRNA gene on the Illumina MiSeq platform. The results of feed microbiota analyses showed that the PM10 feed exhibited a higher microbial diversity than the FM diet. However, these feed-associated microbiota differences were not mirrored in the composition of digesta and mucosal communities. Regardless of the diet, the digesta samples consistently exhibited higher species richness and diversity than the mucosa samples. Overall, digesta samples were characterized by a higher abundance of Firmicutes in PM-fed fish. In contrast, at the gut mucosa level, the relative abundances of Mycobacterium, Taeseokella and Clostridium genera were lower in the group fed the PM10 diet. Significant differences in metabolic pathways were also observed between the FM and PM10 groups in both mucosa and digesta samples. In particular, the mucosal pathways of caffeine metabolism, phenylalanine metabolism, and sulfur relay system were significantly altered by PM inclusion. The same trend was observed in the digesta valine, leucine, and isoleucine degradation and secretion pathways. These findings highlight the potential of PM as an alternative functional ingredient in aquafeeds with microbiota modulatory properties that should be further explored in the future.

Aquaculture ecosystem microbiome at the water-fish interface: the case-study of rainbow trout fed with Tenebrio molitor novel diets

BACKGROUND

Sustainable aquaculture relies on multiple factors, including water quality, fish diets, and farmed fish. Replacing fishmeal (FM) with alternative protein sources is key for improving sustainability in aquaculture and promoting fish health. Indeed, great research efforts have been made to evaluate novel feed formulations, focusing especially on the effects on the fish gut microbiome. Few studies have explored host-environment interactions. In the present study, we evaluated the influence of novel insect-based (Tenebrio molitor) fish diets on the microbiome at the water-fish interface in an engineered rainbow trout (Oncorhynchus mykiss) farming ecosystem. Using 16S rRNA gene metabarcoding, we comprehensively analyzed the microbiomes of water, tank biofilm, fish intestinal mucus, fish cutis, and feed samples.

RESULTS

Core microbiome analysis revealed the presence of a highly reduced core shared by all sample sources, constituted by Aeromonas spp., in both the control and novel feed test groups. Network analysis showed that samples were clustered based on the sample source, with no significant differences related to the feed formulation tested. Thus, the different diets did not seem to affect the environment (water and tank biofilm) and fish (cutis and intestinal mucus) microbiomes. To disentangle the contribution of feed at a finer scale, we performed a differential abundance analysis and observed differential enrichment/impoverishment in specific taxa, comparing the samples belonging to the control diet group and the insect-based diet group.

CONCLUSIONS

Omic exploration of the water-fish interface exposes patterns that are otherwise undetected. These data demonstrate a link between the environment and fish and show that subtle but significant differences are caused by feed composition. Thus, the research presented here is a step towards positively influencing the aquaculture environment and its microbiome.

Functional Additives in a Selected European Sea Bass (Dicentrarchus labrax) Genotype: Effects on the Stress Response and Gill Antioxidant Response to Hydrogen Peroxide (H2O2) Treatment

Functional ingredients have profiled as suitable candidates for reinforcing the fish antioxidant response and stress tolerance. In addition, selective breeding strategies have also demonstrated a correlation between fish growth performance and susceptibility to stressful culture conditions as a key component in species domestication processes. The aim of the present study is to evaluate the ability of a selected high-growth genotype of 300 days post-hatch European sea bass (Dicentrarchus labrax) juveniles to use different functional additives as endogenous antioxidant capacity and stress resistance boosters when supplemented in low fish meal (FM) and fish oil (FO) diets. Three isoenergetic and isonitrogenous diets (10% FM/6% FO) were supplemented with 200 ppm of a blend of garlic and Labiatae plant oils (PHYTO0.02), 1000 ppm of a mixture of citrus flavonoids and Asteraceae and Labiatae plant essential oils (PHYTO0.1) or 5000 ppm of galactomannan-oligosaccharides (GMOS0.5). A reference diet was void of supplementation. The fish were fed the experimental diets for 72 days and subjected to a H₂O₂ exposure oxidative stress challenge. The fish stress response was evaluated through measuring the circulating plasma cortisol levels and the fish gill antioxidant response by the relative gene expression analysis of nfΚβ2, il-1b, hif-1a, nd5, cyb, cox, sod, cat, gpx, tnf-1α and caspase 9. After the oxidative stress challenge, the genotype origin determined the capacity of the recovery of basal cortisol levels after an acute stress response, presenting GS fish with a better pattern of recovery. All functional diets induced a significant upregulation of cat gill gene expression levels compared to fish fed the control diet, regardless of the fish genotype. Altogether, suggesting an increased capacity of the growth selected European sea bass genotype to cope with the potential negative side-effects associated to an H₂O₂ bath exposure.

Sustainable Fish Feeds with Insects and Probiotics Positively Affect Freshwater and Marine Fish Gut Microbiota

Aquaculture is the fastest-growing agricultural industry in the world. Fishmeal is an essential component of commercial fish diets, but its long-term sustainability is a concern. Therefore, it is important to find alternatives to fishmeal that have a similar nutritional value and, at the same time, are affordable and readily available. The search for high-quality alternatives to fishmeal and fish oil has interested researchers worldwide. Over the past 20 years, different insect meals have been studied as a potential alternate source of fishmeal in aquafeeds. On the other hand, probiotics-live microbial strains-are being used as dietary supplements and showing beneficial effects on fish growth and health status. Fish gut microbiota plays a significant role in nutrition metabolism, which affects a number of other physiological functions, including fish growth and development, immune regulation, and pathogen resistance. One of the key reasons for studying fish gut microbiota is the possibility to modify microbial communities that inhabit the intestine to benefit host growth and health. The development of DNA sequencing technologies and advanced bioinformatics tools has made metagenomic analysis a feasible method for researching gut microbes. In this review, we analyze and summarize the current knowledge provided by studies of our research group on using insect meal and probiotic supplements in aquafeed formulations and their effects on different fish gut microbiota. We also highlight future research directions to make insect meals a key source of proteins for sustainable aquaculture and explore the challenges associated with the use of probiotics. Insect meals and probiotics will undoubtedly have a positive effect on the long-term sustainability and profitability of aquaculture.

Efficacy of Utilization of All-Plant-Based and Commercial Low-Fishmeal Feeds in Two Divergently Selected Strains of Rainbow Trout (Oncorhynchus mykiss): Focus on Growth Performance, Whole-Body Proximate Composition, and Intestinal Microbiome

The present study aimed to investigate the growth performance, whole-body proximate composition, and intestinal microbiome of rainbow trout strains when selected and non-selected for weight gain on all-plant protein diets. A 2x2 factorial design was applied, where a selected (United States) and a non-selected (ITA) rainbow trout strain were fed using either an all-plant protein (PP) or a commercial low-FM diet (C). Diets were fed to five replicates of 20 (PP) or 25 (C) fish for 105 days. At the end of the trial, growth parameters were assessed, and whole fish (15 pools of three fish/diet) and gut samples (six fish/diet) were collected for whole-body proximate composition and gut microbiome analyses, respectively. Independent of the administered diet, the United States strain showed higher survival, final body weight, weight gain, and specific growth rate when compared to the ITA fish (p < 0.001). Furthermore, decreased whole-body ether extract content was identified in the PP-fed United States rainbow trout when compared to the ITA strain fed the same diet (p < 0.001). Gut microbiome analysis revealed the Cetobacterium probiotic-like genus as clearly associated with the United States rainbow trout, along with the up-regulation of the pathway involved in starch and sucrose metabolism. In summary, the overall improvement in growth performance and, to a lesser extent, whole-body proximate composition observed in the selected rainbow trout strain was accompanied by specific, positive modulation of the intestinal microbiome.

New value from food and industrial wastes - Bioaccumulation of omega-3 fatty acids from an oleaginous microbial biomass paired with a brewery by-product using black soldier fly (Hermetia illucens) larvae

Research on bioconversion based on insects is intensifying as it addresses the problem of reducing and reusing food and industrial waste. To reach this goal, we need to find more means of pairing waste to insects. With this goal, brewers' spent grains (BSG) - a food waste of the brewing industry - paired with the oleaginous biomass of the thraustochytrid Schizochytrium limacinum cultivated on crude glycerol - a major waste of biodiesel production - were successfully used to grow Hermetia illucens larvae. Combining BSG and S. limacinum in the diet in an attempt to design the lipid profile of H. illucens larvae to contain a higher percentage of omega-3 fatty acids is novel. Insect larvae were grown on three different substrates: i) standard diet for Diptera (SD), ii) BSG, and iii) BSG + 10% S. limacinum biomass. The larvae and substrates were analyzed for fatty acid composition and larval growth was measured until 25% of insects reached the prepupal stage. Our data showed that including omega-3-rich S. limacinum biomass in the BSG substrate promoted an increase in larval weight compared to larvae fed on SD or BSG substrates. Furthermore, it was possible, albeit in a limited way, to incorporate omega-3 fatty acids, principally docosahexaenoic acid (DHA) from BSG + S. limacinum substrate containing 20% of DHA into the larval fat (7% DHA). However, H. illucens with this level of DHA may not be suitable if the aim is to get larvae with high omega-3 lipids to feed carnivorous fish.

Impact of polypropylene microplastics and chemical pollutants on European sea bass (Dicentrarchus labrax) gut microbiota and health

Plastic pollution has become a global problem for marine ecosystems. Microplastics (MPs) are consumed by several marine organisms, including benthic and pelagic fish species that confuse them with food sources, thus contributing to bioaccumulation along the food chain. In addition to structural intestinal damage, ingestion of MPs represents a pathway for fish exposure to potentially hazardous chemicals, too. Most of them are endocrine disrupters, genotoxic or induce immune depression in fish. Accordingly, we assessed the combined toxicological effects of microplastics (MPs) and adsorbed pollutants by adding them to marine fish diet. European sea bass (Dicentrarchus labrax) juveniles were fed for 60 days with feeds containing polypropylene MPs, either virgin or contaminated with chemical pollutants (a blend of dichlorodiphenyldichloroethylene, chlorpyrifos, and benzophenone-3). The data demonstrated a synergic action of MPs and chemical pollutants to induce an inflammatory-like response in distal intestine of sea bass as shown by the up regulation of cytokine il-6 and tnf-α expression. Morphological analysis detected the presence of a focus of lymphocytes in anterior and posterior intestinal segments of fish fed with contaminants in the diet. With regard to microbiota, significant changes in bacterial species richness, beta diversity, and composition of gut microbiota were observed as a consequence of both pollutants and polluted MPs ingestion. These perturbations in gut microbial communities, including the reduction of beneficial lactic acid bacteria and the increase in potential pathogenic microorganism (Proteobacteria and Vibrionales), were undeniable signs of intestinal dysbiosis, which in turn confirmed the signs of inflammation caused by pollutants, especially when combined with MPs. The results obtained in this study provide, therefore, new insights into the potential risks of ingesting MPs as pollutant carriers in marine fish.

Intestinal microbial communities of rainbow trout (Oncorhynchus mykiss) may be improved by feeding a Hermetia illucens meal/low-fishmeal diet

With demands and reliance on aquaculture still growing, there are various challenges to allow sustainable growth and the shift from fishmeal (FM) to other protein sources in aquafeed formulations is one of the most important. In this regard, interest in the use of insect meal (IM) in aquafeeds has grown rapidly. Accordingly, the aim of the present study was to assess the effects of dietary IM from Hermetia illucens (Hi) larvae included in a low-FM diet on gut microbial communities of rainbow trout (Oncorhynchus mykiss), in terms of both composition and function of microbiome. A feeding trial was conducted using 192 trout of about 100-g mean initial weight. Fish were fed in quadruplicate (4 tanks/diet) for 131 days with two diets: the control (Ctrl) contained 20% of FM as well as other protein sources, whereas the Hi diet contained 15% of Hi larvae meal to replace 50% of the FM contained in the Ctrl diet. High-throughput sequencing of 16S rRNA gene was used to identify the major feed and gut bacterial taxa, whereas Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis was performed on gut bacterial genomes to identify the major active biological pathways. The inclusion of IM led to an increase in Firmicutes, mainly represented by Bacilli class and to a drastic reduction of Proteobacteria. Beneficial genera, such as Lactobacillus and Bacillus, were enriched in the gut of fish fed with the Hi diet, whereas the number of bacteria assigned to the pathogenic Aeromonas genus was drastically reduced in the same fish group. The metagenome functional data provided evidence that dietary IM inclusion can shape the metabolic activity of trout gut microbiota. In particular, intestinal microbiome of fish fed with IM may have the capacity to improve dietary carbohydrate utilization. Therefore, H. illucens meal is a promising protein source for trout nutrition, able to modulate gut microbial community by increasing the abundance of some bacteria taxa that are likely to play a key role in fish health.

Effects of full replacement of dietary fishmeal with insect meal from Tenebrio molitor on rainbow trout gut and skin microbiota

Background

Aquaculture must continue to reduce dependence on fishmeal (FM) and fishoil in feeds to ensure sustainable sector growth. Therefore, the use of novel aquaculture feed ingredients is growing. In this regard, insects can represent a new world of sustainable and protein-rich ingredients for farmed fish feeds. Accordingly, we investigated the effects of full replacement of FM with Tenebrio molitor (TM) larvae meal in the diet of rainbow trout (Oncorhynchus mykiss) on fish gut and skin microbiota.

Methods

A feeding trial was conducted with 126 trout of about 80 g mean initial weight that were fed for 22 weeks with two isonitrogenous, isolipidic, and isoenergetic extruded experimental diets. Partially defatted TM meal was included in one of the diets to replace 100% (TM 100) of FM, whereas the other diet (TM 0) was without TM. To analyse the microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and Qiime pipeline were used to identify bacteria in the gut and skin mucosa, and in the diets.

Results

The data showed no major effects of full FM substitution with TM meal on bacterial species richness and diversity in both, gut mucosa- and skin mucus-associated microbiome. Skin microbiome was dominated by phylum Proteobacteria and especially by Gammaproteobacteria class that constituted approximately half of the bacterial taxa found. The two dietary fish groups did not display distinctive features, except for a decrease in the relative abundance of Deefgea genus (family Neisseriaceae) in trout fed with insect meal. The metagenomic analysis of the gut mucosa indicated that Tenericutes was the most abundant phylum, regardless of the diet. Specifically, within this phylum, the Mollicutes, mainly represented by Mycoplasmataceae family, were the dominant class. However, we observed only a weak dietary modulation of intestinal bacterial communities. The only changes due to full FM replacement with TM meal were a decreased number of Proteobacteria and a reduced number of taxa assigned to Ruminococcaceae and Neisseriaceae families.

Conclusions

The data demonstrated that TM larvae meal is a valid alternative animal protein to replace FM in the aquafeeds. Only slight gut and skin microbiota changes occurred in rainbow trout after total FM replacement with insect meal. The mapping of the trout skin microbiota represents a novel contribution of the present study. Indeed, in contrast to the increasing knowledge on gut microbiota, the skin microbiota of major farmed fish species remains largely unmapped but it deserves thorough consideration.

Effect of dietary oil from Camelina sativa on the growth performance, fillet fatty acid profile and gut microbiome of gilthead Sea bream (Sparus aurata)

BACKGROUND

In the last two decades, research has focused on testing cheaper and sustainable alternatives to fish oil (FO), such as vegetable oils (VO), in aquafeeds. However, FO cannot be entirely replaced by VOs due to their lack of omega-3 (n-3) long-chain polyunsaturated fatty acids (LC-PUFA), particularly eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3) acids. The oilseed plant, Camelina sativa, may have a higher potential to replace FO since it can contains up to 40% of the omega-3 precursors α-linolenic acid (ALA; 18:3n-3) and linoleic acid (LA; 18:2n-6).

METHODS

A 90-day feeding trial was conducted with 600 gilthead sea bream (Sparus aurata) of 32.92 ±  0.31 g mean initial weight fed three diets that replaced 20%, 40% and 60% of FO with CO and a control diet of FO. Fish were distributed into triplicate tanks per diet and with 50 fish each in a flow-through open marine system. Growth performance and fatty acid profiles of the fillet were analysed. The Illumina MiSeq platform for sequencing of 16S rRNA gene and Mothur pipeline were used to identify bacteria in the faeces, gut mucosa and diets in addition to metagenomic analysis by PICRUSt.

RESULTS AND CONCLUSIONS

The feed conversion rate and specific growth rate were not affected by diet, although final weight was significantly lower for fish fed the 60% CO diet. Reduced final weight was attributed to lower levels of EPA and DHA in the CO ingredient. The lipid profile of fillets were similar between the dietary groups in regards to total saturated, monounsaturated, PUFA (n-3 and n-6), and the ratio of n-3/n-6. Levels of EPA and DHA in the fillet reflected the progressive replacement of FO by CO in the diet and the EPA was significantly lower in fish fed the 60% CO diet, while ALA was increased. Alpha and beta-diversities of gut bacteria in both the faeces and mucosa were not affected by any dietary treatment, although a few indicator bacteria, such as Corynebacterium and Rhodospirillales, were associated with the 60% CO diet. However, lower abundance of lactic acid bacteria, specifically Lactobacillus, in the gut of fish fed the 60% CO diet may indicate a potential negative effect on gut microbiota. PICRUSt analysis revealed similar predictive functions of bacteria in the faeces and mucosa, although a higher abundance of Corynebacterium in the mucosa of fish fed 60% CO diet increased the KEGG pathway of fatty acid synthesis and may act to compensate for the lack of fatty acids in the diet. In summary, this study demonstrated that up to 40% of FO can be replaced with CO without negative effects on growth performance, fillet composition and gut microbiota of gilthead sea bream.

Effects of Partially Defatted Hermetia illucens Meal in Rainbow Trout Diet on Hepatic Methionine Metabolism

Simple Summary

For sustainable aquaculture development, fish meal from the sea in aquafeed should be replaced with other sustainable materials such as insect larvae. The authors fed black soldier fly maggot meal to rainbow trout and examined the expression of three genes and two metabolites involved in turn-over of methionine that is an essential amino acid in fish. According to the increase in the maggot content in the aquafeed, gene expression was modulated to maintain an optimal level of methionine metabolites. Dietary replacement of up to 50% of fish meal with the maggot meal was acceptable, implying future development of a new aquafeed for sustainable aquaculture.

Abstract

This study investigated, for the first time, the effects of replacement of fishmeal (FM) with insect meal from Hermetia illucens (HI) on the transcript levels of three genes involved in methionine (Met) metabolism in rainbow trout (Oncorhynchus mykiss) liver. Two target genes—betaine-homocysteine S-methyltransferase (BHMT) and S-adenosylhomocysteine hydrolase (SAHH)—are involved in Met resynthesis and the third one—cystathionine β synthase (CBS)—is involved in net Met loss (taurine synthesis). We also investigated the levels of two Met metabolites involved in the maintenance of methyl groups and homocysteine homeostasis in the hepatic tissue: S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). Three diets were formulated, an FM-based diet (HI0) and two diets in which 25% (HI25) and 50% (HI50) of FM was replaced with HI larvae meal. A 78-day feeding trial involved 360 rainbow trout with 178.9 ± 9.81 g initial average weight. Dietary replacement of up to 50% of FM with HI larvae meal, without any Met supplementation, did not negatively affect rainbow trout growth parameters and hepatic Met metabolism. In particular, Met availability from the insect-based diets directly modulated the transcript levels of two out of three target genes (CBS, SAHH) to maintain an optimal level of one-carbon metabolic substrates, i.e., the SAM:SAH ratio in the hepatic tissue.

Can intestinal absorption of dietary protein be improved through early exposure to plant-based diet?

Nutritional Programming (NP) has been studied as a means of mitigating the negative effects of dietary plant protein (PP), but the optimal timing and mechanism behind NP are still unknown. The objectives of this study were: 1) To determine whether zebrafish (Danio rerio) can be programmed to soybean meal (SBM) through early feeding and broodstock exposure to improve SBM utilization; 2) To determine if NP in zebrafish affects expression of genes associated with intestinal nutrient uptake; 3) To determine if early stage NP and/or broodstock affects gene expression associated with intestinal inflammation or any morphological changes in the intestinal tract that might improve dietary SBM utilization. Two broodstocks were used to form the six experimental groups. One broodstock group received fishmeal (FM) diet (FMBS), while the other was fed ("programmed with") SBM diet (PPBS). The first ((+) Control) and the second group ((-) Control) received FM and SBM diet for the entire study, respectively, and were progeny of FMBS. The last four groups consisted of a non-programmed (FMBS-X-PP and PPBS-X-PP) and a programmed group (FMBS-NP-PP and PPBS-NP-PP) from each of the broodstocks. The programming occurred through feeding with SBM diet during 13-23 dph. The non-control groups underwent a PP-Challenge, receiving SBM diet during 36-60 dph. During the PP-Challenge, both PPBS groups experienced significantly lower weight gains than the (+) Control group. NP in early life stages significantly increased the expression of PepT1 in PPBS-NP-PP, compared to PPBS-X-PP. NP also tended to increase the expression of fabp2 in the programmed vs. non-programmed groups of both broodstocks. The highest distal villus length-to-width ratio was observed in the dual-programmed group, suggesting an increase in surface area for nutrient absorption within the intestine. The results of this study suggest that NP during early life stages may increase intestinal absorption of nutrients from PP-based feeds.

Effects of hydrolyzed fish protein and autolyzed yeast as substitutes of fishmeal in the gilthead sea bream (Sparus aurata) diet, on fish intestinal microbiome

Background

This study evaluated the effects of partial substitution of dietary fishmeal (FM) with either fish protein hydrolysate (FPH) or autolysed dried yeast (HiCell®, Biorigin, Brazil) on intestinal microbiota of gilthead sea bream (Sparus aurata). A total number of 720 fish of 122.18 ± 6.22 g were fed for 92 days with three different diets in triplicate (3 tanks/diet). A diet based on FM/vegetable meal was used as control. The other two diets were formulated by replacing FM with 5% of either FPH or HiCell®. To analyze the gut microbiota associated to autochthonous and allochthonous microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and QIIME pipeline were used.

Results

A total number of 102 OTUs (operational taxonomic units) at 97% identity were identified in fish gut samples collected at the end of feeding trial. Fourteen OTUs constituted the core gut microbiota, i.e. those OTUs found in at least nine out of fifteen samples per group and shared regardless of the diet. Eight OTUs were assigned to Firmicutes represented by Lactobacillus, Staphylococcus, and Bacillus genera, and six to Proteobacteria phylum. Dietary dried yeast autolysate modulated the intestinal microbiota by promoting the growth of some beneficial bacteria. At order level, fish fed yeast showed an enrichment in Bacillales and Clostridiales as compared to the control group, whereas fish fed FPH showed a significantly lower amount of bacteria belonging to Alteromonadales and Enterobacteriales than the other two feeding groups. Although we did not observe any effect of 5% FM replacement with alternative nitrogen sources at phylum level, at lower taxonomical levels, the composition of gut microbiota, in terms of relative abundance of specific taxa, was significantly influenced by the dietary treatment.

Conclusions

The metabarcoding analysis revealed a clearly intestinal microbiota modulation in response to dietary autolyzed yeast. The abundance of some beneficial bacteria, i.e. indigestible carbohydrate degrading- and SCFA producing bacteria, was positively affected. Brewer’s yeast autolysate could be a valid alternative protein source to FM as well as a valid functional ingredient for aquafeed production.

Assessment of dietary supplementation with galactomannan oligosaccharides and phytogenics on gut microbiota of European sea bass (Dicentrarchus Labrax) fed low fishmeal and fish oil based diet

There is an increasing interest from the aquafeed industry in functional feeds containing selected additives that improve fish growth performance and health status. Functional feed additives include probiotics, prebiotics, organic acids, and phytogenics (substances derived from plants and their extracts). This study evaluated the effects of dietary inclusion of a mucilage extract rich in galactomannan oligosaccharides (GMOS), a mixture of garlic and labiatae-plants oils (PHYTO), and a combination of them (GMOSPHYTO), on gut microbiota composition of European sea bass (Dicentrarchus labrax) fed with a low fishmeal (FM) and fish oil (FO) diet. Three experimental diets and a control diet (plant-based formulation with 10% FM and 6% FO) were tested in a 63-days feeding trial. To analyze the microbiota associated to feeds and the intestinal autochthonous (mucosa-adhered) and allochthonous (transient) microbial communities, the Illumina MiSeq platform for sequencing of 16S rRNA gene and QIIME2 pipeline were used. Metabarcoding analysis of feed-associated bacteria showed that the microbial communities of control (CTRL) feed deeply differed from those of experimental diets. The number of reads was significantly lower in CTRL feed than in other feeds. The OTU (operational taxonomic unit) number was instead similar between the feeds, ranging from 42 to 50 OTUs. The variation of resident gut microbiota induced by diet was lower than the variation of transient intestinal microbiota, because feedstuffs are a major source of allochthonous bacteria, which can temporarily integrate into the gut transient microbiome. However, the composition of transient bacterial communities was not simply a mirror of feed-borne bacteria. Indeed, the microbial profile of feeds was different from both faecal and mucosa profiles. Our findings suggest that the dietary inclusion of GMOS (0.5%) and PHYTO (0.02%) in a low FM and FO diet induces changes in gut microbiota composition of European sea bass. However, if on allochthonous microbiota the combined inclusion of GMOS and PHYTO showed an antagonistic effect on bactericidal activity against Vibrionales, at mucosa level, only GMOSPHYTO diet increased the relative abundance of Bacteroidales, Lactobacillales, and Clostridiales resident bacterial orders. The main beneficial effects of GMOS and PHYTO on gut microbiota are the reduction of coliforms and Vibrionales bacteria, which include several potentially pathogenic species for fish, and the enrichment of gut microbiota composition with butyrate producer taxa. Therefore, these functional ingredients have a great potential to be used as health-promoting agents in the farming of European sea bass and other marine fish.

Nano-delivery of trace minerals for marine fish larvae: influence on skeletal ossification, and the expression of genes involved in intestinal transport of minerals, osteoblast differentiation, and oxidative stress response

Currently, the larviculture of many marine fish species with small-sized larvae depends for a short time after hatching, on the supply of high-quality live zooplankton to ensure high survival and growth rates. During the last few decades, the research community has made great efforts to develop artificial diets, which can completely substitute live prey. However, studies aimed at determining optimal levels of minerals in marine larvae compound feeds and the potential of novel delivery vectors for mineral acquisition has only very recently begun. Recently, the agro-food industry has developed several nano-delivery systems, which could be used for animal feed, too. Delivery through nano-encapsulation of minerals and feed additives would protect the bioactive molecules during feed manufacturing and fish feeding and allow an efficient acquisition of active substances into biological system. The idea is that dietary minerals in the form of nanoparticles may enter cells more easily than their larger counterparts enter and thus speed up their assimilation in fish. Accordingly, we evaluated the efficacy of early weaning diets fortified with organic, inorganic, or nanoparticle forms of trace minerals (Se, Zn, and Mn) in gilthead seabream (Sparus aurata) larvae. We tested four experimental diets: a trace mineral-deficient control diet, and three diets supplemented with different forms of trace minerals. At the end of the feeding trial, larvae growth performance and ossification, and the level of expression of six target genes (SLC11A2β, dmt1, BMP2, OC, SOD, GPX), were evaluated. Our data demonstrated that weaning diets supplemented with Mn, Se, and Zn in amino acid-chelated (organic) or nanoparticle form were more effective than diets supplemented with inorganic form of minerals to promote bone mineralization, and prevent skeletal anomalies in seabream larvae. Furthermore, nanometals markedly improved larval stress resistance in comparison to inorganic minerals and upregulated mRNA copy number of OC gene. The expression of this gene was strongly correlated with mineralization degree, thus confirming its potency as a good marker of bone mineralization in gilthead seabream larvae.

Effect of a specific composition of short- and medium-chain fatty acid 1-Monoglycerides on growth performances and gut microbiota of gilthead sea bream (Sparus aurata)

In aquaculture research, one important aim of gut microbiota studies is to provide the scientific basis for developing effective strategies to manipulate gut microbial communities through the diet, promoting fish health and improving productivity. Currently, there is an increasing commercial and research interest towards the use of organic acids in aquafeeds, due to several beneficial effects they have on growth performance and intestinal tract's health of farmed fish. Among organic acids, monoglycerides of short-chain fatty acids (SCFAs) and medium-chain fatty acids (MCFAs) have attracted particular research attention also for their bacteriostatic and bactericidal properties. Accordingly, the present study aimed to evaluate the potential beneficial effects of SCFA and MCFA monoglycerides, used as a feed additive, on fish growth performance, and intestinal microbiota composition. For this purpose, a specific combination of short- and medium-chain 1-monoglycerides (SILOhealth 108Z) was tested in 600 juvenile gilthead sea bream (Sparus aurata) of about 60 g mean initial weight that were fed for 90 days with plant-based diets. Two isoproteic and isolipidic diets were formulated. The control fish group received a plant-based diet, whereas the other group received the same control feed, but supplemented with 0.5% of SILOhealth 108Z. The Illumina MiSeq platform for high-throughput amplicon sequencing of 16S rRNA gene and QIIME pipeline were used to analyse and characterize the whole microbiome associated both to feeds and S. aurata intestine. The number of reads taxonomically classified according to the Greengenes database was 394,611. We identified 259 OTUs at 97% identity in sea bream fecal samples; 90 OTUs constituted the core gut microbiota. Firmicutes, Proteobacteria and Actinobacteria represented the dominant phyla in both experimental groups. Among them, relative abundance of Firmicutes and Proteobacteria were positively and negatively affected by dietary SCFA monoglycerides supplementation, respectively. In summary, our findings clearly indicated that SILOhealth 108Z positively modulated the fish intestinal microbiota by increasing the number of beneficial lactic acid bacteria, namely, Lactobacillus, and reducing Gammaproteobacteria, which include several potential pathogenic bacteria. The specific composition of 1-monoglycerides of short- and medium-chain fatty acids contained in SILOhealth 108Z could thus have a great potential as a feed additive in aquaculture.

Next generation sequencing for gut microbiome characterization in rainbow trout (Oncorhynchus mykiss) fed animal by-product meals as an alternative to fishmeal protein sources

Animal by-product meals from the rendering industry could provide a sustainable and commercially viable alternative to fishmeal (FM) in aquaculture, as they are rich in most essential amino acids and contain important amounts of water-soluble proteins that improve feed digestibility and palatability. Among them, poultry by-product meal (PBM) have given encouraging results in rainbow trout (Oncorhynchus mykiss). However, the introduction of new ingredients in the diet needs to be carefully evaluated since diet is one of the main factors affecting the gut microbiota, which is a complex community that contributes to host metabolism, nutrition, growth, and disease resistance. Accordingly, we investigated the effects of partial replacement of dietary FM with a mix of animal by-product meals and plant proteins on intestinal microbiota composition of rainbow trout in relation to growth and feeding efficiency parameters. We used 1540 trout with an initial mean body weight of 94.6 ± 14.2 g. Fish were fed for 12 weeks with 7 different feed formulations. The growth data showed that trout fed on diets rich in animal by-product meals grew as well as fish fed on control diet, which was rich in FM (37.3%) and PBM-free. High-throughput 16S rRNA gene amplicon sequencing (MiSeq platform, Illumina) was utilised to study the gut microbial community profile. After discarding Cyanobacteria (class Chloroplast) and mitochondria reads a total of 2,701,274 of reads taxonomically classified, corresponding to a mean of 96,474 ± 68,056 reads per sample, were obtained. Five thousand three hundred ninety-nine operational taxonomic units (OTUs) were identified, which predominantly mapped to the phyla of Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria. The ratio between vegetable and animal proteins proved to play a central role in determining microbiome profiles and Firmicutes and Proteobacteria phyla were particularly discriminatory for diet type in trout. Plant ingredients favoured a higher Firmicutes:Proteobacteria ratio than animal proteins. Acceptable abundance of Firmicutes was guaranteed by including at least 25% of vegetable proteins in the diet regardless of animal protein source and percentage. In summary animal by-product meals, as replacements to FM, gave good results in terms of growth performances and did not induce significant changes in gut microbial richness, thus proving to be a suitable protein source for use in rainbow trout aqua feed.

Inorganic, organic, and encapsulated minerals in vegetable meal based diets for Sparus aurata (Linnaeus, 1758)

Substituting fishmeal (FM) with vegetable meal (VM) can markedly affect the mineral composition of feeds, and may require additional mineral supplementation. Their bioavailability and optimal supplementation levels depend also on the form of delivery of minerals. The aim of the study was to determine the effect of different delivery forms of three major trace elements (Zn, Mn and Se) in a marine teleost. Gilthead sea bream juveniles of 22.5 g were fed a VM-based diet for 12 weeks that was either not supplemented with these minerals or supplemented with inorganic, organic, or encapsulated inorganic forms of minerals in triplicate and compared to a FM-based diet. Our results showed that mineral delivery form significantly affected the biochemical composition and morphology of posterior vertebrae. Supplementation of VM-based diets with inorganic forms of the target minerals significantly promoted growth, increased the vertebral weight and content of ash and Zn, enhanced bone mineralization and affected the vertebral shape. Conversely, encapsulation of inorganic minerals reduced fish growth and vertebral mineral content, whereas supplementation of organic minerals, enhanced bone osteogenesis by upregulating bone morphogenetic protein 2 (bmp2) gene and produced vertebrae with a larger length in relation to height. Furthermore, organic mineral forms of delivery downregulated the expression of oxidative stress related genes, such as Cu/Zn superoxide dismutase (Cu/Zn sod) and glutathione peroxidase 1 (gpx-1), suggesting thus that dietary minerals supplemented in the organic form could be reasonably considered more effective than the inorganic and encapsulated forms of supply.

The expression of hypoxia-inducible factor-1α gene is not affected by low-oxygen conditions in yellow perch (Perca flavescens) juveniles

Hypoxia can affect various fish populations, including yellow perch Perca flavescens, which is an economically and ecologically important species in Lake Erie, a freshwater system that often experiences hypoxia in the hypolimnetic part of the lake. Fish, similarly to mammals, possess molecular oxygen sensor-hypoxia-inducible factor-1 (HIF-1), a transcription factor that can affect expression of many downstream genes related to animal growth and locomotion, protein synthesis, as well as ATP and amino acid metabolism. HIF-1 is a heterodimer, which consists of two subunits: oxygen-sensitive and oxygen-insensitive subunits, α and β, respectively. In this study, we report first on the molecular cloning and sequencing of P. flavescens HIF-1α. The full-length complementary DNA (cDNA) was isolated and submitted to the GenBank with accession number KT783483. It consists of 3529 base pairs (bp) carrying a single open-reading frame that encompasses 2250 bp of the coding region, 247 bp of the 5' untranslated region (UTR), and 1032 bp of the 3' UTR. The "de novo" prediction of the 3D structure of HIF-1α protein, which consists of 749 amino acids, is presented, too. We then utilized One-Step Taqman® real-time RT-PCR technology to monitor changes in HIF-1α messenger RNA (mRNA) copies in response to chronic hypoxic stress. An experiment was conducted using 14-day post-swim-up stage yellow perch larvae with uninflated swim bladders. This experiment included three treatment groups: hypoxia, mid-hypoxia, and normoxia, in four replicates (four tanks per treatment) with the following dissolved oxygen levels: 3, 4, and >7 mg O₂/L, respectively. At the end (2 weeks) and in the middle (1 week) of the experiment, fish from each tank were sampled for body measurements and molecular biology analysis. The results showed no differences in survival (∼90%) between treatment groups. Oxygen concentration was lowered to 3.02 ± 0.15 (mean ± SE) mg O₂/L with no adverse effect on fish survival. The highest growth rate was observed in the normoxic group. A similar trend was observed with fish body length. The growth rate of fish declined with decreasing water-dissolved oxygen. The number of HIF-1α mRNA copies was not significantly different between hypoxic, mid-hypoxic, and normoxic conditions, and this was true for fish obtained in the middle and at the end of the experiment. Graphical abstract.

Skin Mucus of Gilthead Sea Bream (Sparus aurata L.). Protein Mapping and Regulation in Chronically Stressed Fish

The skin mucus of gilthead sea bream was mapped by one-dimensional gel electrophoresis followed by liquid chromatography coupled to high resolution mass spectrometry using a quadrupole time-of-flight mass analyzer. More than 2,000 proteins were identified with a protein score filter of 30. The identified proteins were represented in 418 canonical pathways of the Ingenuity Pathway software. After filtering by canonical pathway overlapping, the retained proteins were clustered in three groups. The mitochondrial cluster contained 59 proteins related to oxidative phosphorylation and mitochondrial dysfunction. The second cluster contained 79 proteins related to antigen presentation and protein ubiquitination pathways. The third cluster contained 257 proteins where proteins related to protein synthesis, cellular assembly, and epithelial integrity were over-represented. The latter group also included acute phase response signaling. In parallel, two-dimensional gel electrophoresis methodology identified six proteins spots of different protein abundance when comparing unstressed fish with chronically stressed fish in an experimental model that mimicked daily farming activities. The major changes were associated with a higher abundance of cytokeratin 8 in the skin mucus proteome of stressed fish, which was confirmed by immunoblotting. Thus, the increased abundance of markers of skin epithelial turnover results in a promising indicator of chronic stress in fish.

Effects of Sodium Butyrate Treatment on Histone Modifications and the Expression of Genes Related to Epigenetic Regulatory Mechanisms and Immune Response in European Sea Bass (Dicentrarchus Labrax) Fed a Plant-Based Diet

Bacteria that inhabit the epithelium of the animals' digestive tract provide the essential biochemical pathways for fermenting otherwise indigestible dietary fibers, leading to the production of short-chain fatty acids (SCFAs). Of the major SCFAs, butyrate has received particular attention due to its numerous positive effects on the health of the intestinal tract and peripheral tissues. The mechanisms of action of this four-carbon chain organic acid are different; many of these are related to its potent regulatory effect on gene expression since butyrate is a histone deacetylase inhibitor that play a predominant role in the epigenetic regulation of gene expression and cell function. In the present work, we investigated in the European sea bass (Dicentrarchus labrax) the effects of butyrate used as a feed additive on fish epigenetics as well as its regulatory role in mucosal protection and immune homeostasis through impact on gene expression. Seven target genes related to inflammatory response and reinforcement of the epithelial defense barrier [tnfα (tumor necrosis factor alpha) il1β, (interleukin 1beta), il-6, il-8, il-10, and muc2 (mucin 2)] and five target genes related to epigenetic modifications [dicer1(double-stranded RNA-specific endoribonuclease), ehmt2 (euchromatic histone-lysine-N-methyltransferase 2), pcgf2 (polycomb group ring finger 2), hdac11 (histone deacetylase-11), and jarid2a (jumonji)] were analyzed in fish intestine and liver. We also investigated the effect of dietary butyrate supplementation on histone acetylation, by performing an immunoblotting analysis on liver core histone extracts. Results of the eight-week-long feeding trial showed no significant differences in weight gain or SGR (specific growth rate) of sea bass that received 0.2% sodium butyrate supplementation in the diet in comparison to control fish that received a diet without Na-butyrate. Dietary butyrate led to a twofold increase in the acetylation level of histone H4 at lysine 8, but showed no effect on the histone H3 at Lys9. Moreover, two different isoforms of histone H3 that might correspond to the H3.1 and H3.2 isoforms previously found in terrestrial animals were separated on the immunoblots. The expression of four (il1 β, il8, irf1, and tnfα) out of seven analyzed genes related to mucosal protection and inflammatory response was significantly different between the two analyzed tissues but only il10 showed differences in expression due to the interaction between tissue and butyrate treatment. In addition, butyrate caused significant changes in vivo in the expression of genes related to epigenetic regulatory mechanisms such as hdac11, ehmt2, and dicer1. Statistical analysis by two-way ANOVA for these genes showed not only significant differences due to the butyrate treatment, but also due to the interaction between tissue and treatment.

Amino acid transporter B(0)AT1 (slc6a19) and ancillary protein: impact on function

Amino acids play an important role in the metabolism of all organisms. Their epithelial re-absorption is due to specific transport proteins, such as B(0)AT1, a Na(+)-coupled neutral amino acid symporter belonging to the solute carrier 6 family. Here, a recently cloned fish orthologue, from the intestine of Salmo salar, was electrophysiologically characterized with the two-electrode voltage clamp technique, in Xenopus laevis oocytes heterologously expressing the transporter. Substrate specificity, apparent affinities and the ionic dependence of the transport mechanism were determined in the presence of specific collectrin. Results demonstrated that like the human, but differently from sea bass (Dicentrarchus labrax) orthologue, salmon B(0)AT1 needs to be associated with partner proteins to be correctly expressed at the oocyte plasma membrane. Cloning of sea bass collectrin and comparison of membrane expression and functionality of the B(0)AT1 orthologue transporters allowed a deeper investigation on the role of their interactions. The parameters acquired by electrophysiological and immunolocalization experiments in the mammalian and fish transporters contributed to highlight the dynamic of relations and impacts on transport function of the ancillary proteins. The comparative characterization of the physiological parameters of amino acid transporters with auxiliary proteins can help the comprehension of the regulatory mechanism of essential nutrient absorption.

The Effect of Hypoxia and Hyperoxia on Growth and Expression of Hypoxia-Related Genes and Proteins in Spotted Gar Lepisosteus oculatus Larvae and Juveniles

We studied the molecular responses to different water oxygen levels in gills and swim bladder of spotted gar (Lepisosteus oculatus), a bimodal breather. Fish at swim-up stage were exposed for 71 days to normoxic, hypoxic, and hyperoxic water conditions. Then, all aquaria were switched to normoxic conditions for recovery until the end of the experiment (120 days). Fish were sampled at the beginning of the experiment, and then at 71 days of exposure and at 8 days of recovery. We first cloned three hypoxia-related genes, hypoxia-inducible factor 2α (HIF-2α), Na(+) /H(+) exchanger 1 (NHE-1), and NHE-3, and uploaded their cDNA sequences in the GeneBank database. We then used One Step Taqman® real-time PCR to quantify the mRNA copies of target genes in gills and swim bladder of fish exposed to different water O2 levels. We also determined the protein expression of HIF-2α and neuronal nitric oxide synthase (nNOS) in the swim bladder by using confocal immunofluorescence. Hypoxic stress for 71 days significantly increased the mRNA copies of HIF-2α and NHE-1 in gills and swim bladder, whereas normoxic recovery for 8 days decreased the HIF-2α mRNA copies to control values in both tissues. We did not found significant changes in mRNA copies of the NHE-3 gene in either gills or swim bladder in response to hypoxia and hyperoxia. Unlike in normoxic swim bladder, double immunohistochemical staining in hypoxic and hyperoxic swim bladder using nNOS/HIF-2α showed extensive bundles of HIF-2α-positive nerve fibers in the trabecular musculature associated with a few varicose nNOS immunoreactive nerve terminals.

Activity, Expression, and Substrate Preference of the Δ(6)-Desaturase in Slow- or Fast-Growing Rabbit Genotypes

In the present paper liver fatty acid Δ(6) desaturation (fads2) activity was analyzed in two rabbit strains with slow- (S, 27.5 g/day) or fast-growing (F, 48.5 g/day) rate. The fatty acid profile of the liver showed a different PUFA profile in the two strains with a lower n-6/n-3 ratio in the S rabbits. The expression of fads2 was 2-fold higher in S than in F rabbits, whereas enzyme activity was higher in F and more oriented toward the desaturation of linoleic acid (90%). In contrast, S showed a higher preference for linolenic acid (38.9 vs 10%). This study identified a single difference in the fads2 amino acid sequence between these two strains. Such a difference consists in the substitution of Gly104 to Ser104 in the sequence of F fads2. These results indicate for the first time that genetic selection for performance may affect the preference for PUFA toward desaturation of linoleic/linolenic acid.

Expression profile of six stress-related genes and productive performances of fast and slow growing broiler strains reared under heat stress conditions

High temperature is one of the prominent environmental factors causing economic losses to the poultry industry as it negatively affects growth and production performance in broiler chickens. We used One Step TaqMan real time RT-PCR (reverse transcription polymerase chain reaction) technology to study the effects of chronic heat stress on the expression of genes codifying for the antioxidative enzymes superoxide dismutase (SOD), and catalase (CAT), as well as for heat shock protein (HSP) 70, HSP90, glucocorticoid receptor (NR3C1), and caspase 6 (CASP6) in the liver of two different broiler genetic strains: Red JA Cou Nu Hubbard (CN) and Ross 508 Aviagen (RO). CN is a naked neck slow growing broiler intended for the free range and/or organic markets, whereas RO is selected for fast growing. We also analysed the effect of chronic heat stress on productive performances, and plasma corticosterone levels as well as the association between transcriptomic response and specific SNPs (single nucleotide polymorphisms) in each genetic strain of broiler chickens. RO and CN broilers, 4 weeks of age, were maintained for 4 weeks at either 34 °C or 22 °C. The results demonstrated that there was a genotype and a temperature main effect on the broilers' growth from the 4th to the 8th week of age, but the interaction effect between genotype and temperature resulted not statistically significant. By considering the genotype effect, fast growing broilers (RO) grew more than the slow growing ones (CN), whereas by considering the temperature effect, broilers in unheated conditions grew more than the heat stressed ones. Corticosterone levels increased significantly in the blood of heat stressed broilers, due to the activation of the HPA (hypothalamic-pituitary-adrenocortical axis). Carcass yield at slaughter was of similar values in the 4 cohorts (genotype/temperature combinations or treatment groups), ranging from 86.5 to 88.6%, whereas carcass weight was negatively influenced by heat stress in both broiler strains. Heat stress affected gene expression by downregulating CASP6 and upregulating CAT transcript levels. HSPs, SOD and NR3C1 mRNA levels remained unaffected by heat stress. The differences found in the mRNA copies of CASP6 gene could be partly explained by SNPs.

Modulation of adrenocorticotrophin hormone (ACTH)-induced expression of stress-related genes by PUFA in inter-renal cells from European sea bass (Dicentrarchus labrax)

Dietary fatty acids have been shown to exert a clear effect on the stress response, modulating the release of cortisol. The role of fatty acids on the expression of steroidogenic genes has been described in mammals, but little is known in fish. The effect of different fatty acids on the release of cortisol and expression of stress-related genes of European sea bass (Dicentrarchus labrax) head kidney, induced by a pulse of adenocorticotrophin hormone (ACTH), was studied. Tissue was maintained in superfusion with 60 min of incubation with EPA, DHA, arachidonic acid (ARA), linoleic acid or α-linolenic acid (ALA) during 490 min. Cortisol was measured by RIA. The quantification of stress-related genes transcripts was conducted by One-Step TaqMan real-time RT-PCR. There was an effect of the type of fatty acid on the ACTH-induced release of cortisol, values from ALA treatment being elevated within all of the experimental period. The expression of some steroidogenic genes, such as the steroidogenic acute regulatory protein (StAR) and c-fos, were affected by fatty acids, ALA increasing the expression of StAR after 1 h of ACTH stimulation whereas DHA, ARA and ALA increased the expression of c-fos after 20 min. ARA increased expression of the 11β-hydroxylase gene. Expression of heat shock protein 70 (HSP70) was increased in all the experimental treatments except for ARA. Results corroborate previous studies of the effect of different fatty acids on the release of cortisol in marine fish and demonstrate that those effects are mediated by alteration of the expression of steroidogenic genes.

Molecular cloning, characterization and expression analysis of ATG1 in the silkworm, Bombyx mori

Atg1 is a Serine/Threonine protein kinase that plays a pivotal role in autophagy. A complete coding sequence of ATG1 is not available for the silkworm, Bombyx mori which is a good model for studying the autophagic process. In the present study we isolated two full-length cDNAs of 2175 (transcript variant A) and 2271 (transcript variant B) bases representing ATG1 in the silkworm. Phylogenetic analysis indicated that BmATG1 was closely related to orthologs of other insects. The encoded BmAtg1 proteins shared extensive homology with orthologs from yeast to mammals, showing high conservation at the N-terminal region where the catalytic domain and ATP- and Mg-binding sites are located. A de novo prediction of the three-dimensional structure for each protein is presented. We used real-time RT-PCR to quantify dynamic changes in mRNA copy number of BmATG1 in the midgut and fat body of fifth instar larvae undergoing starvation, as well as in other tissues of silkworm at the end of last larval instar. Our qPCR results revealed that BmATG1 expression levels at the end of larval life were comparable in the midgut, fat body and Malpighian tubules, while these were higher in the gonads; moreover, the mRNA copy number of ATG1 was very different among the anterior, middle and posterior silk glands. Real-time PCR analysis also showed that starvation significantly influenced BmATG1 mRNA copy number in the fat body of silkworm, inducing an upregulation 24h after food withdrawal, with only a slight effect in the midgut. Low expression levels of BmATG1 were observed in both tissues of control animals up to the second day of spinning phase.

HIF-1α mRNA levels in Eurasian perch (Perca fluviatilis) exposed to acute and chronic hypoxia

The big advantage of using molecular biomarkers to monitor oxygen levels in aquatic systems is that responses at the molecular level tend to be more sensitive, and usually occur earlier than those at higher levels of biological organization Aquatic hypoxia is a frequent event, which can occur naturally in a variety of marine, estuarine and freshwater habitats. More often, however, hypoxia arises as a result of euthrophication of aquatic ecosystem and can lead to changes in community structure by eliminating hypoxia-sensitive species. Consequently fish have develop various physiological and biochemical mechanisms to cope with this environmental stress. Many of these adjustments depend to changes in expression of a wide range of genes. The transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor-1 (HIF-1), a heterodimer composed of an α and β subunit. This study investigated if HIF-1α mRNA levels were regulated by hypoxia in Eurasian perch (Perca fluviatilis), a hypoxia-sensitive fresh water species. The real-time PCR was utilized to monitor dynamic changes in levels of HIF-1α mRNA in response to acute (DO 0.4 ± 0.1 mg/l for 1 h) and chronic (DO 2.8 ± 0.3 mg/l for 15 days) hypoxia. Our results indicated an up-regulation of HIF-1α in brain and liver, but not in muscle tissue after acute hypoxic treatment, whereas significant changes of HIF-1α mRNA levels were detected in muscle, but not in brain and liver after chronic hypoxia exposure. This study suggests that HIF-1α mRNA level in selected perch tissues could be an useful indicator of acute exposure to hypoxia.

Bio-Mos: an effective inducer of dicentracin gene expression in European sea bass (Dicentrarchus labrax)

Concern over the use of dietary antibiotics in aquaculture has encouraged the industry to search for alternatives that both enhance performance and afford protection from disease. Bio-Mos, derived from the outer cell wall of a specific strain of yeast Saccharomyces cerevisiae (Alltech Inc, USA) is a product that fits these criteria. Here, we present data on the impact of a Bio-Mos supplemented diet on the mRNA copy number of the antimicrobial peptide dicentracin, whose transcript regulation has not yet been explored in fish.We analyzed Bio-Mos-induced changes in the expression of sea bass (Dicentrarchus labrax) dicentracin,using a one-tube two-temperature real-time RT-PCR with which the gene expression can be absolutely quantified using the standard curve method. Our results revealed that 30 days of feeding fish with diets containing Bio-Mos supplemented at either 3 per thousand or 5 per thousand significantly increased the dicentracin mRNA copy number in the head kidney. Furthermore, the mRNA copy number in fish fed at 3 per thousand was significantly higher than that of the group fed at 5 per thousand for the same period of feeding Bio-Mos. A longer feeding period (60 days)did not further increase the dicentracin transcript levels as compared to the values recorded after 30 days of feeding either in the group fed at 3 per thousand or in the one fed at 5 per thousand diet. However, the transcript levels in fish fed at 3 per thousand proved to be significantly higher than those of the controls after 60 days of feeding. These findings offer new information about the response of antimicrobial peptides at the transcriptional level to diets supplemented with immune response modulators, and support a role of Bio-Mos in promoting sea bass nonspecific immune system.

Sea bass ghrelin: molecular cloning and mRNA quantification during fasting and refeeding

Ghrelin is a novel appetite-inducing peptide hormone secreted by the stomach. The purpose of this study was first to identify the cDNA encoding sequence for ghrelin in sea bass (Dicentrarchus labrax). Using molecular cloning techniques we sequenced the cDNA corresponding to sea bass ghrelin mRNA. A total of 798 bases including a 5'-untranslated region (89 bp), an open reading frame (ORF) (324 bp), and a 3'-untranslated region (385 bp) were detected. Nucleotide sequence (ORF) encoded a 108 amino acid prepropeptide that demonstrated complete conservation of the N-terminal "biological active core" (GSSF) of the predicted mature ghrelin peptide. We also analyzed fasting-induced changes in the expression of ghrelin mRNA, using a one-tube two-temperature real-time RT-PCR with which the gene expression can be absolutely quantified using the standard curve method. Our results revealed that ghrelin was highly expressed in the stomach with much lower levels of expression in the proximal intestine and brain. Levels of ghrelin mRNA in the stomach were upregulated under conditions of negative energy balance, such as starvation, and downregulated during positive energy balance, such as refeeding. These findings offer new information about the sea bass ghrelin gene and support a role of this orexigenic hormone in the regulation of food intake in sea bass.

Regulation of progastricsin mRNA levels in sea bass (Dicentrarchus labrax) in response to fluctuations in food availability

In this study the sea bass (Dicentrarchus labrax) pepsinogen C gene was isolated. The nucleotide sequences of all exons are presented. The organization of the gene is compatible with that of other aspartic proteinases. The predicted 388-residue amino acid (aa) sequence of sea bass pepsinogen C consists of a signal sequence of 16 amino acid residues, an activation peptide of 43 residues, and the mature pepsin of 329 residues containing the two characteristic active-site aspartic acids. We also analyzed fasting-induced changes in the expression of progastricsin mRNA, using real-time RT-PCR absolute quantification. Progastricsin mRNA copy number was downregulated under conditions of negative energy balance, such as starvation, and upregulated during positive energy balance, such as refeeding. These findings offer new information about the sea bass progastricsin gene and support a role of this gastric digestive enzyme in the regulation of food intake in sea bass.

Evaluation of SAT-1, SAT-2 and GalNAcT-1 mRNA in colon cancer by real-time PCR

By qualitative and quantitative PCR, we evaluated the expression of three messengers coding for SAT-1, SAT-2 and GalNAcT-1 in human samples of intestinal cancer and some cell lines (breast cancer and melanomas). Qualitative PCR demonstrated, in human tissues but not in the cell lines examined, the presence of an mRNA that lacks hexon 3; experiments performed on transfected SKMEL-28 excluded a regulative role of this noncanonical mRNA. Data from real-time PCR, statistically analysed by ANOVA indicated that the mRNA expression of all the considered glycosyltransferases (SAT-1, SAT-2 and GalNAcT-1) was significantly different in tumours versus their own control. The ganglioside patterns in the examined samples did not correlate with mRNA expression; this finding demonstrates that ganglioside expression is the result of a very complex balance between anabolic and catabolic enzyme activities. Although this study is still preliminary, it opens a new possibility for neoplastic prognosis finding potential molecular markers among the mRNAs that codify for glycosyltransferases.

Molecular cloning and expression of alpha2,8-sialyltransferase (ST8Sia I, GD3 Synthase) in Xenopus

GD3, a minor ganglioside in most normal tissues, is involved in important biological events and its expression could increase in pathological conditions. Organism integrity requires a tight balance between the anabolic and catabolic processes, thus it is important to control the intracellular expression of those "key" enzymes, which act at the "branching point" of ganglioside metabolism; one of these is the GD3-synthase (ST8Sia I). In this paper, we report the sequences of two ST8Sia I mRNAs found in Xenopus laevis and their genomic organization; the canonical form resulted constituted of 5 exons and 4 introns, while the "short" mRNA lacks of the exon 2. The expression of the two ST8Sia I mRNAs during embryo development and their tissue distribution in adult animals showed the single or simultaneous presence of the two forms. Experiments of in vitro expression and evaluation of enzymatic activity of the two hypothetical proteins turned out to be ST8Sia I. In the end, considering the growing interest toward the specie Xenopus tropicalis, due to its diploid genome that render it more suitable for genetic studies, we also cloned X. tropicalis ST8Sia I.

EST-based identification of genes expressed in the liver of adult seabass (Dicentrarchus labrax, L.)

The scarcity of the genomic resources for some fish species, in spite of their commercial interest, could retard the positive effects that modern biotechnology can offer to aquaculture industry. Then an effort should be made to reduce, as far as it concerns genomic resources, the gap that separates farming species from "model organisms". In this paper, we present an EST project in which we performed single pass sequencing on 1229 randomly selected clones from a sea bass cDNA library. The sequences are deposited in the NCBI database with the following accession numbers: from , from , from and from . EST cataloguing and profiling of seabass will set the basis for functional genomic research in this species, but will also serve for comparative and environmental genomics, for the identification of polymorphic markers useful, for example, to survey the disease resistance of fish, for the discovery of new molecular markers of exposure and for the production of micro- and macro-arrays.

Quantification of a glucocorticoid receptor in sea bass (Dicentrarchus labrax, L.) reared at high stocking density

To assess the effects of environmental stress conditions on fish, the examination of a suite of biomarkers, including endocrine parameters, has been suggested. In teleosts, glucocorticoids, including cortisol and corticosterone, are known to mediate stress response. Inside the cell, they bind to a high-affinity cytosolic glucocorticoid receptor (GR), which acts as ligand-dependent transcription factor to control and regulate gene expression. Receptor number or affinity may directly influence the degree of reactivity of target cells. GR transcripts have been cloned and characterized in different fish species, but no studies, to date, are available on the quantification of GR in sea bass (Dicentrarchus labrax, L.), although this is one of the most important species in Mediterranean aquaculture. These considerations prompted our interest in cloning the GR in this species and investigating the impact of long-term exposure to crowding stress on GR expression in the liver of sea bass. Our data clearly demonstrate that a high rearing density stress affects GR mRNA, whose abundance in the liver decreased inversely with blood cortisol levels.

Molecular markers for animal biotechnology: sea bass (Dicentrarchus labrax, L.) HMG-CoA reductase mRNA

Modern technologies may improve fish production and quality and, at the same time, reduce environmental impact with benefits on the public perception of the industry. To be economically profitable, these modern technologies request an increase of rearing density that, however, could affect fish welfare. With the aim to search for molecular biomarkers to describe fish welfare, we have recently compared gene expression of sea bass farmed at different population densities by differential display obtaining six bands differentially expressed. In this paper, we have cloned the mRNA corresponding to one of those differentially expressed bands obtaining a 3860-bp sequence with an ORF of 2664 bp. Its virtual translation originated a 887-aa polypeptide that, by comparison with the other sequences available in the public data bases, resulted to be the 3-hydroxil-3-methyl-glutaryl coenzyme A reductase (HMGCR). In sea bass, as for the other species, the N- and C-terminus portions are the most conserved and are linked by an hydrophilic region that appears to be quite variable. Due to its role in the synthesis of cholesterol, HMGCR mRNA could be a good biomarker for detecting fish welfare. For this reason, we also followed, by real-time PCR, its expression after crowding stress comparing it with mRNA levels of HSP 70 and 90: HMGCR mRNA resulted highly expressed in the fishes farmed at 100 kg/m(3).